i have Vox VT20+ and i would like to buy a distortion pedal.
i like very much the big muff by electroharmonix. will it be compatible with my amp?

I've read some posts that there wont be any issues,but i want to be 100% sure before i buy it .

Thank you for your time.
Your amp already has distortion effects built in. It even has a fuzz effect which is probably modeled after the Big Muff.

Solid State/Modeler amps (like the VT20+) do not take pedals as well as tube amps do, generally. The Big Muff is not really that expensive (especially if you buy used) so it is not too steep of a loss. But really I would just save up for a better amp that will take pedals better.
buying a new amp isnt an option at the moment.
i have tryied the fuzz effect but i dont like it very much.i guess ill give it a try then